Methods and systems for in-situ extraction of bitumen

ABSTRACT

Methods and systems for in situ extraction of bitumen from deposits of bitumen-containing material are described. The methods and systems can generally include establishing freeze walls within the deposit of bitumen-containing material to establish a confined zone into which solvents can be injected in order to extract bitumen from the bitumen-containing deposits. Different types of solvents can be sequentially injected in order to extract bitumen and also help reduce the amount of solvent left behind in the deposit.

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/522,904, filed Aug. 12, 2011, the entirety of which is herebyincorporated by reference.

BACKGROUND

Deposits of bituminous material can be found throughout the world,including in the United States and Canada. Depending on the depth of thebituminous material, various methods can be used to extract bitumen frombituminous deposits. When the bituminous material is located relativelyclose to the surface, surface mining can be used to remove thebituminous material from the ground. However, deeper deposits ofbituminous material cannot be economically obtained through surfacemining. Accordingly, methods involving the use of well bores drilledinto the bituminous deposits have been developed.

One such method for obtaining deeper deposits of bituminous material isthe Steam Assisted Gravity Drainage (SAGD) method. The SAGD methodgenerally includes injecting steam into the bituminous deposit to warmthe bituminous material and make it flowable. Once the viscosity of thebituminous material is sufficiently lowered, the bituminous material canflow downwardly to a horizontal production well that is positioned belowthe horizontal well used to inject steam into the deposit. While theSAGD method can be relatively effective in extracting bituminousmaterial from bitumen deposits, other methods that do not require theuse of water and that provide better bitumen extraction rates aredesired.

The use of solvents to extract bitumen from mined oil sands or the likeis considered an effective method for separating bitumen from othercomponents of the oil sands material. The solvent is generally used todissolve the bitumen, after which the bitumen-loaded solvent isseparated from the sand, clay, and other components of the oil sands.The injection of solvent into a deposit of oil sands to dissolve thebitumen would appear to be an effective means for extracting bitumenfrom a bituminous deposit, but several problems are associated withsolvent injection into the ground that have prevented the method frombeing feasible.

One primary problem with injecting solvent into the oil sands deposit isthat it has been difficult or impossible to recover a sufficient amountof the injected solvent to make the process economical. For example, insome instances, only 25% of the solvent injected into the deposit can berecovered. The cost of having to replenish large amounts of solvent tocontinue the process generally makes the process uneconomical.

An additional problem with injecting solvent into the oil sands depositsrelates to the environmental concerns of injecting potentially hazardoussolvent material into the ground without any effective way of recoveringthe solvent or preventing the solvent from migrating to a locationoutside of the oil sands deposit. For example, if the oil sands depositis near an aquifer, then concerns arise regarding the flow of solventout of the oils sands deposit and into the aquifer, where potential wellwater would be contaminated.

SUMMARY

The foregoing and other features, utilities and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

In some embodiments, a method of in-situ bitumen extraction isdisclosed, the method including a step of forming one or more verticalfreeze walls within or around a deposit of bituminous material andestablishing a laterally confined deposit of bituminous material; a stepof injecting a first solvent within the laterally confined deposit ofbituminous material; a step of withdrawing a mixture of dissolvedbitumen and first solvent from within the laterally confined deposit ofbituminous material; a step of injecting a second solvent within thelaterally confined deposit of bituminous material; a step of withdrawinga mixture of first solvent and second solvent from within the laterallyconfined deposit of bituminous material; a step of injecting waterwithin the laterally confined deposit of bituminous material; and a stepof withdrawing a mixture of second solvent and water from within thelaterally confined deposit of bituminous material.

In some embodiments, a system for in-situ bitumen extraction isdisclosed, the system including a plurality of vertical freeze wallbores formed in a deposit of bituminous material and aligned in ageometric pattern; a refrigerant source in fluid communication with theplurality of vertical freeze wall bores; a plurality of verticalinjection bores formed win the deposit of bituminous material andlocated within the geometric pattern of the plurality of freeze walls; awater source in fluid communication with the plurality of verticalinjection bores; a first solvent source in fluid communication with theplurality of vertical injection bores; optionally a second solventsource in fluid communication with the plurality of vertical injectionbores; and a plurality of vertical production wells formed in thedeposit of bituminous material and located within the geometric patternof the plurality of freeze walls.

The foregoing and other features and advantages of the presentapplication will become more apparent from the following detaileddescription, which proceeds with reference to the accompanying figures.In this regard, it is to be understood that the scope of the inventionis to be determined by the claims as issued and not by whether givensubject includes any or all features or aspects noted in this Summary oraddresses any issues noted in the Background.

BRIEF DESCRIPTION OF THE DRAWING

The preferred and other embodiments are disclosed in association withthe accompanying drawings in which:

FIG. 1 is flow chart of embodiments of an in-situ bitumen extractionmethod described herein;

FIG. 2 is an aerial view of a configuration of well bores formed in adeposit of bituminous material in accordance with some embodimentsdescribed herein;

FIG. 3 is an aerial view of a configuration of well bores formed in adeposit of bituminous material, including a two loop refrigerantcirculation system according to some embodiments described herein;

FIG. 4 is a cross-sectional view of a bituminous deposit having avertical injection well and a vertical production well formed therein inaccordance with some embodiments described herein;

FIG. 5 is a cross-sectional view of a bituminous deposit having ahorizontal injection well and a horizontal production well formedtherein in accordance with some embodiments described herein; and

FIG. 6 is a cross-sectional view of a composite injection according tosome embodiments described herein.

DETAILED DESCRIPTION

With reference to FIG. 1, some embodiments of a method of in-situextraction of bitumen generally include a step 100 of forming one ormore vertical freeze walls within or around a deposit of bituminousmaterial and establishing a laterally confined deposit of bituminousmaterial, a step 110 of injecting a first solvent within the laterallyconfined deposit of bituminous material, a step 120 of withdrawing amixture of dissolved bitumen and first solvent from within the laterallyconfined deposit of bituminous material, a step 130 of injecting asecond solvent within the laterally confined deposit of bituminousmaterial, a step 140 of withdrawing a mixture of first solvent andsecond solvent from within the laterally confined deposit of bituminousmaterial, a step 150 of injecting water within the laterally confineddeposit of bituminous material, and a step 160 of withdrawing a mixtureof second solvent and water from within the laterally confined depositof bituminous material. Such embodiments can successfully confinematerial injected into the bituminous deposit within a prescribed area.Similarly, mixtures of dissolved bitumen and solvent created byinjecting material into the bituminous deposit are maintained within thearea defined by the freeze walls. Accordingly, contamination of, forexample, underground water sources can be mitigated or prevented andrecovery of dissolved bitumen can be enhanced by providing barriersaround the bitumen deposit being subjected to the bitumen extractionprocesses.

In step 100, one or more vertical freeze walls are formed within oraround a deposit of bituminous material. The vertical freeze wallsformed within or around the deposit of bituminous material form aboundary around all or a portion of the deposit of bituminous materialand establish a laterally confined deposit of bituminous material. Anobjective of step 100 is to provide vertical boundaries that willprevent material injected into the deposit of bituminous material andmixture of materials formed within the bituminous deposit from travelingoutside of the laterally confined area, thus alleviating environmentalconcerns of in-situ bitumen extraction and making collection ofdissolved bitumen easier.

The deposit of bituminous material in which the vertical freeze wallsare formed in step 100 can be any suitable deposit of bituminousmaterial. Suitable deposits of bituminous material include tar sands oroil sands formations, such as those located in the Athabasca region ofCanada. In some embodiments, the deposit of bituminous material is adeposit or a portion for a deposit that is located at a depth that istoo deep for surface mining but too shallow for traditional in-situbitumen extraction methods such as stream assisted gravity drainage(SAGD). In some embodiments, the deposit of bituminous material islocated at a depth of from between 250 feet and 1,500 feet below thesurface.

The one or more freeze walls formed in the deposit of bituminousmaterial can be any type of freeze wall capable of slowing or preventingthe movement of fluids through the freeze wall. The freeze walls aretypically made from water that is naturally present in the ground in aliquid form. By freezing this water, a barrier of ice is created in theground. Freeze walls can be formed in deposits of bituminous materialbecause bituminous material (such as oil sands deposits) typicallyincludes a water content.

Any manner of forming the one or more freeze walls known to those ofordinary skill in the art can be used in the embodiments of this method.In an exemplary method, a series of interconnected vertical well boresare constructed within or around the deposit of bituminous material, anda refrigerant is circulated through the vertical well bores until thewater in the ground proximate the vertical well bores freezes. Therefrigerant can be continuously circulated through the vertical wellbores to ensure the water remains frozen and the freeze walls remainintact. Any suitable refrigerant can be used, such as brine or ammonia.In some embodiments, the refrigerant is circulated within the well boresfor a period of from 6 weeks to 16 weeks in order to establish thefreeze walls.

The arrangement and spacing of the vertical well bores within or aroundthe deposit of bituminous material can be any suitable arrangement forproviding freeze walls. In some embodiments, the vertical well bores arespaced close enough together that the water in the area between twoadjacent vertical well bores can be frozen to create a vertical freezewall. In some embodiments, the well bores are spaced apart approximately2 to 6 meters from one another.

The dimensions of the well bores can vary based on the specificapplication but are typically selected to ensure that a suitable amountof refrigerant passes through the well bores to freeze the water in thesurrounding ground. In some embodiments, the well bores have a diameterin the range of from 3 to 15 inches. The depth of the well bores can bedependent on a variety of factors. In some embodiments, the depth of thewell bores is selected based on the depth of the deposit of bituminousmaterial and/or the depth of any bed rock or other geological formationthat might be located beneath the deposit of bituminous material. A bedrock or other geological formation below the deposit of bituminousmaterial can serve as a lower horizontal boundary for the deposit ofbituminous material, so it can be beneficial to extend the well boresdown to abut a rock formation or the like. Generally speaking, the wellbores will have a depth of from 100 to 1,500 feet.

In some embodiments, the vertical well bores are arranged in a closedgeometric pattern (when looking down at the vertical well bores fromabove) to thereby create vertical freeze walls that enclose a deposit ofbituminous material. Any suitable closed geometric shape can be used.With reference to FIG. 2, the vertical well bores 200 are arranged in arectangular shape, with each side of the rectangle including severalwell bores 200. The well bores 200 are spaced close enough to freeze thearea 210 between each well bore 200 and ultimately form a series ofvertical freeze walls arranged in a rectangular shape and enclosing adeposit of bituminous material 220.

The well bores used to form the freeze walls are generally constructedby drilling vertical holes into the deposit of bituminous material andproviding piping within the drilled holes. The piping can be anysuitable type of piping, but is typically of a type that is impermeableto fluids and has good heat transfer for allowing the refrigerant tofreeze the water proximate the piping. The piping may also havestructural additions to improve heat transfer, such as a plurality offins extending out from the piping. As noted above, the piping providedin the drilled holes can be interconnected with piping in adjacentdrilled holes such that the refrigerant can circulate throughout theplurality of well bores.

In some embodiments, the well bores constructed for establishing freezewalls in the deposit of bituminous material can include a two loopsystem of interconnected well bores. The two loop system allows forrefrigerant to be supplied into the interconnected well bores in a firstloop and for refrigerant to be removed from the interconnected wellbores in a second loop. With reference to FIG. 3, the two loop system300 provides a first loop 310 where refrigerant is introduced into thesystem to flow through the well bores 350 and create and/or maintainfreeze walls. The first loop 310 extends around the closed geometricarrangement of well bores 350 and is in fluid communication 315 witheach of the well bores 350 such that refrigerant introduced into thefirst loop 310 can travel to each of the well bores 350 and providerefrigerant into the well bores 350. The two loop system also includes asecond loop 320. Like first loop 310, second loop 320 extends around theclosed geometric arrangement of well bores 350 and is in fluidcommunication 325 with each of the well bores 350. Second loop 320receives refrigerant that has flowed through the well bores 350 andprovides a path 360 for the refrigerant to leave the system 300. In someembodiments, the first loop 310 will be in fluid communication at abottom end of each well bore 350 and the second loop 320 will be influid communication with the top end of each well bore 350 such that newrefrigerant is introduced into each well bore 350 at the bottom via thefirst loop 310 and then exits the well bore 350 at the top via thesecond loop 320. The opposite arrangement can also be used. The two loopsystem 300 provides a manner for fresh refrigerant to be introduced intothe system and for used refrigerant to be taken out of the system, whereit can be reconditioned and reinjected back into the well bores 350.

Well bores as described above are not the only mechanism that can beused to create the freeze walls in step 110. In some embodiments, freezewalls can be formed using thermosyphons. Thermosyphons generally includea fully enclosed system having a low temperature fluid (such as liquidCO₂, or ammonia) circulating inside. Natural convection allows theliquid to pick up heat from the bed rock at the bottom of the closedsystem below and convert to a vapor. The vapor rises to the top of thesystem, where cooling occurs (such as wind cooling via radiators) toconvert the vapor back to liquid. The cooled liquid drains back to thebottom of the system, and the process repeats.

As noted above, bed rock or other geological formations can be used toserve as a lower horizontal barrier of the confined deposit ofbituminous material. However, natural barriers may not always beavailable. Accordingly, in some embodiments, steps can also be taken toform a horizontal freeze wall that will serve as a barrier thatvertically confines the deposit of bituminous material. Generallyspeaking, such a horizontal freeze wall will extend up to or beyond thevertical freeze walls laterally confining the deposit of bituminousmaterial. It can also be preferable to have the horizontal freeze wallabut the bottom end of the vertical freeze walls. In this manner, thematerial injected into the confined deposit of bituminous material willbe prevented from leaving the confined area in both a lateral directionand in a downward direction.

Any suitable manner of forming horizontal freeze walls can be used. Insome embodiments, the manner of forming the horizontal freeze wall issimilar or identical to the manner in which the vertical freeze wallsare used. For example, directional drilling techniques can be used toform a plurality of horizontal well bores through which refrigerant canflow in order to freeze the water in the ground between adjacenthorizontal well bores.

In step 100, the vertical freeze walls formed serve to laterally confinea deposit of bituminous material. When bed rock (or other geologicalformation) or a horizontal freeze wall are used in conjunction with thevertical freeze walls, a “bath tub” configuration is provided that iscapable of retaining liquid material within the confined “bath tub”area. Accordingly, when solvents are injected into the confined area ofbituminous material, the “bath tub” configuration mitigates oreliminates concerns related to injected solvent drifting out of the areaundergoing bitumen extraction and into, for example, underground watersources. Similarly, the “bath tub” configuration helps to keep dissolvedbitumen within a confined area, which helps make withdrawing dissolvedbitumen from the deposit of bituminous material more effective andefficient.

In step 110, a first solvent is injected into the laterally confineddeposit of bituminous material. The injected first solvent is injectedto dissolve bitumen and create a dissolved bitumen (or “disbit”) phasewithin the deposit. Once dissolved, the mixture of bitumen and solventcan be withdrawn from the deposit to thereby extract bitumen.

The first solvent used in step 110 may include a hydrocarbon solvent.Any hydrocarbon solvent or mixture of hydrocarbon solvents that iscapable of dissolving bitumen can be used. In some embodiments, thehydrocarbon solvent is a hydrocarbon solvent that does not result inasphaltene precipitation. The hydrocarbon solvent or mixture ofhydrocarbon solvents can be economical and relatively easy to handle andstore. The hydrocarbon solvent or mixture of hydrocarbon solvents mayalso be generally compatible with refinery operations.

In some embodiments, the first solvent is a light aromatic solvent. Thelight aromatic solvent is an aromatic compound having a boiling pointtemperature less than about 400° C. at atmospheric pressure. In someembodiments, the light aromatic solvent used in the first mixing step isan aromatic having a boiling point temperature in the range of fromabout 75° C. to about 350° C. at atmospheric pressure, and morespecifically, in the range of from about 100° C. to about 250° C. atatmospheric pressure.

It should be appreciated that the light aromatic solvent need not be100% aromatic compounds. Instead, the light aromatic solvent may includea mixture of aromatic and non-aromatic compounds. For example, the firstsolvent can include greater than zero to about 100 wt % aromaticcompounds, such as approximately 10 wt % to 100 wt % aromatic compounds,or approximately 20 wt % to 100 wt % aromatic compounds.

Any of a number of suitable aromatic compounds may be used as the firstsolvent. Examples of aromatic compounds that can be used as the firstsolvent include benzene, toluene, xylene, aromatic alcohols andcombinations and derivatives thereof. The first solvent can also includecompositions, such as kerosene, diesel (including biodiesel), light gasoil, light distillate, commercial aromatic solvents such as Solvesso100, Solvesso 150, and Solvesso 200 (also known in the U.S.A. asAromatic 100, 150, and 200, including mainly C₁₀-C₁₁ aromatics, andproduced by ExxonMobil), and/or naphtha. In some embodiments, the firstsolvent may have a boiling point temperature of approximately 75° C. to375° C. Naphtha, for example, is particularly effective at dissolvingbitumen and is generally compatible with refinery operations.

In some embodiments, a portion or all of the first solvent is derivedfrom bitumen recovered by the in-situ bitumen extraction processdescribed herein. The bitumen extracted by the process described hereincan be subjected to distillation processing to separate a light endportion of the bitumen that is suitable for use as a first solvent inthe process described herein. In some embodiments, the light end portionof the recovered bitumen is a fraction of the bitumen having a boilingpoint temperature in the range of up to 225° C.

Any distillation methods capable of separating fractions of bitumenmaterial known to those of ordinary skill in the art can be used,including the use of atmospheric or vacuum distillation towers. In someembodiments, a make-up first solvent, such as any of the above discussedfirst solvents, can be mixed with the light end portion of the bitumenin order to provide a suitable amount of first solvent for the process.Obtaining a portion or all of the first solvent from the bitumenrecovered by the in-situ bitumen extraction process described herein canbe useful in that the process can become essentially self-sustainable.Additionally, use of first solvent derived from the recovered bitumencan reduce or eliminate environmental concerns associated with usingnon-indigenous or commercial solvents.

In some embodiments, the first solvent suitable for use in step 110includes a bitumen content, and can therefore be considered as disbit ordilbit. The first solvent having a bitumen content may be solventobtained from a step of solvent extraction process performed onbituminous material, such as tar sands or oil sands.

The amount of first solvent injected into the laterally confined depositof bituminous material can be any suitable amount of first solventneeded for dissolving bitumen. In some embodiments, the amount ofsolvent injected into the deposit of bituminous material will depend onthe quality of the deposit of bituminous material (i.e., the bitumencontent of the bituminous material). Larger bitumen contents can requirelarger amounts of first solvent to ensure as much bitumen as possible isdissolved into a disbit phase. The amount of first solvent injected intothe deposit of bituminous material can also vary on the size of the areabeing subjected to bitumen extraction. In some embodiments, the amountof first solvent injected into the deposit ranges from 0.5:1 to 5:1.

In some embodiments, the desired amount of first solvent is injectedinto the deposit of bituminous material and is then allowed to stay inthe deposit of bituminous material for a period of time beforeproduction wells are used to remove any disbit formed. Holding the firstsolvent into the deposit of bituminous material allows for the firstsolvent to migrate to a larger area and have sufficient time to dissolvethe bitumen. In some embodiments, the first solvent is held in thedeposit of bituminous material for a period of from 1 day to 1 month.

Any suitable technique for injecting solvent into the laterally confineddeposit of bituminous material can be used in step 110. In someembodiments, one or more injection wells are formed in the laterallyconfined area, which allows for solvent to flow down and into thebituminous material bound by the freeze walls. Once the solvent isinjected into the confined deposit of bituminous material, the solventworks to dissolve the bitumen and create a disbit phase within thedeposit of bituminous material. The injection wells can be paired withproduction wells capable of drawing the disbit phase out of the depositof bituminous material and up to the surface.

The injection wells can be any type of injection wells suitable forinjecting solvent into a deposit of bituminous material, and can beconstructed by any suitable technique used by those or ordinary skill inthe art to construct injection wells. Similarly, production wells usedto draw fluid material out of the deposit of bituminous material (suchas disbit) can be any suitable type of production well and can beconstructed by any suitable technique for constructing production wells.In some embodiments, the injection wells and productions wells aresimilar enough that injection wells can be transformed into productionwells with minimal modifications.

The dimensions of the production wells and injection wells can be anysuitable dimensions needed to carry out the in-situ bitumen extraction.The length of the injection wells and the production wells willgenerally be equal to or slightly shorter than the depth of the depositof bituminous material. The diameter of the injection wells andproduction wells can vary, and in some embodiments, range from 6 to 12inches.

With reference to FIG. 4, the injection wells formed in the laterallyconfined area can be vertical injection wells 410 that have a pluralityof injection ports 415 located along the height of the injection well410 for injecting solvent into the deposit of bituminous material 400 atvarious depths. The injection ports 415 are capable of injecting solventinto the deposit of bituminous material 400, and in some cases willgenerally inject solvent into the bituminous deposit 400 at a directionperpendicular to the vertical injection well 410. The vertical injectionwells 410 can be paired with vertical production wells 430 that arespaced apart a distance from the injection wells 410. In this manner,the vertical production wells can collect the mixture of solvent anddissolved bitumen produced upon injecting solvent into the deposit ofbituminous material 400.

With reference to FIG. 5, the injection wells formed in the laterallyconfined area can also be a series of horizontal injection wells 510.The horizontal injection wells 510 generally have an L-shapedconfiguration that includes a vertical portion 510 a and a horizontalportion 510 b. Solvent travels down into the deposit of bituminousmaterial 500 via the vertical portion 510 a and is injected into thedeposit of bituminous material 500 via the horizontal portion 510 b. Insome embodiments, a plurality of injection ports 515 are located alongthe length of the horizontal portion 510 b of the horizontal injectionwell 510 such that solvent is injected into the deposit of bituminousmaterial 500 at various locations along the length of the horizontalportion 510 b of the horizontal injection well 510. In some embodiments,the injection ports 515 are oriented to inject solvent upwardly into thebituminous deposit 500. Horizontal production wells 530 can also beincluded to withdraw the disbit formed upon the injection of solventinto the deposit of bituminous material 500 via the horizontal injectionwell 510. In some embodiments, the horizontal production wells 530 havea vertical portion 530 a and horizontal portion 530 b. The horizontalportion 530 b can be located parallel to and below the horizontalportion 510 b of the horizontal injection well 510. The disbit formedabove the horizontal portion 510 b flows downwardly where it collectedin the horizontal portion 530 b of the horizontal production well 530.The collected disbit is then transported up the vertical portion 530 aof the horizontal production well 530 to the surface.

The injection wells and production wells are formed within the area ofbituminous material confined by the freeze walls established in step100. The arrangement of the plurality of injection wells and productionwells is generally not limited and can include any arrangement that willprovide for multiple solvent injection locations and multiple disbitproduction locations. Generally speaking, the injection wells andproduction wells are located close enough to one another that theproduction wells can receive the disbit created by injecting solventinto the deposit of bituminous material via the injection wells. In someembodiments, a production well is located from 50 to 100 feet from aninjection well.

In some embodiments, more injection wells than production wells will beprovided within the deposit of bituminous material confined by thefreeze walls, such as from 2 to 6 injection wells per production well.The arrangement of injection wells and production wells can includevarious geometric shapes and patterns. One exemplary arrangementinvolves a hexagonal matrix of production wells surrounding an injectionwell located in the middle of the hexagon.

In some embodiments where vertical injection wells and production wellsare used, the arrangement of injection wells and production wells can bea straight line arrangement of injection wells and a straight linearrangement of production wells parallel to the injection wells andspaced apart a suitable distance. The straight lines of injection wellsand production wells can be located relatively close to one of thefreeze walls making up the boundary of the confined deposit ofbituminous material, and can also be oriented in parallel to that freezewall. Thus, for example, in a rectangular shaped confined deposit ofbituminous material, a straight line of injection wells can be locatednext to and in parallel with a freeze wall, while a straight line ofproduction wells can be located next to and in parallel with thestraight line of injection wells, and further away from the freeze wallthen the injection wells. The injection ports on the injection wells canbe pointed in a direction towards the production wells (i.e., away fromthe freeze wall) to extract bitumen from the area closest to the freezewall. Once this area has been sufficiently treated, the injection wellscan be decommissioned, the production wells can be converted toinjection wells (including positioning injection ports in a directionaway from the freeze wall), and a new straight line of production wellscan be formed further into the confined area and in parallel with thestraight line of injection wells. The space between the new injectionwells and the new production wells can be treated for a sufficientperiod of time, after which the above described process of convertingproduction wells into injection wells and forming new production wellsis repeated. This cycle can be repeated until the entire length of therectangular confined area is subjected to bitumen extraction. Such asystem can be referred to as a “line drive” process of extractingbitumen.

In some embodiments, the injection of first solvent is followed by anagitation step in order to promote mixing between the solvent and thebituminous material. Any suitable manner of causing agitation within thebituminous deposit can be used. In some embodiments, the agitation stepincludes a gas injection or gas pulsation step. In both gas injectionand gas pulsation, the introduction of the gas into the deposit leads toimproved mixing between the solvent and the bituminous material, whichin turn leads to more bitumen dissolving in the solvent.

The gas injection or gas pulsation step can be carried out using theinjection wells described in greater detail above. For example, in gasinjection, the gas is injected into the deposit via the same injectionwells used to inject the solvent into the bituminous deposit. Any gassuitable for use in agitating the solvent in the bituminous deposit canbe used. In some embodiments, the gas is unreactive to the materials inthe bituminous deposit such that the injection of the gas leads toprimarily the mechanical agitation of the solvent and not to thereaction between the gas and the solvent or materials in the bituminousdeposit. Exemplary gasses that can be used include but are not limitedto natural gas, nitrogen, air, and carbon dioxide.

In some embodiments, the gas is preferably injected into the bituminousdeposit at relatively high volumes to ensure agitation. In someembodiments, the gas is injected into the bituminous deposit at a rateof 0.20 to 1.45 BCFD (depending on the geologic conditions and oilproduction rate) or, in some embodiments, from 130 BOPD to 600 BOPD perMMCFD of gas injected. When gas pulsation is used, the frequency of thegas pulsation can be between 2 and 10 Hz. The injection of first solventinto the bituminous deposit can be carried out in several cycles, and insome embodiments, the agitation step is carried out after every cycle ofinjecting first solvent into the bituminous deposit.

In step 120, a mixture of first solvent and dissolved bitumen producedfrom injecting solvent into the deposit of bituminous material in step110 is withdrawn from within the laterally confined deposit ofbituminous material. Any suitable manner of withdrawing the disbit fromwithin the deposit of bituminous material can be used to carry out step120. As discussed in greater detail above, in some embodiments thedisbit is withdrawn from within the deposit of bituminous material usingproduction wells that are located proximate the injection wells.Production wells can be operated for extended periods of time, such asup to 9 months, to ensure that the vast majority of the disbit producedin step 110 is withdrawn from the deposit. In some embodiments, theproduction wells are operated until 90% of the disbit produced in step110 is removed. Step 120 is usually performed after step 110 iscompleted, but is some embodiments, step 120 can be commenced prior tostep 110 being completed.

The fluid material withdrawn from within the deposit of bituminousmaterial in step 120 generally includes first solvent and dissolvedbitumen. Other materials that can be present in the fluid materialinclude water, and organic and inorganic solids. Generally speaking, thefluid material withdrawn in step 120 includes from 40 to 75% firstsolvent, from 25 to 60% bitumen, from 0 to 5% water, and less than 2%other materials. The rate of withdrawing the fluid material is generallynot limited, and in some embodiments, the fluid is withdrawn from withinthe deposit of bituminous material via the production wells at a rate offrom about 5,000 to 25,000 bbls/day.

Once the mixture of dissolved bitumen and first solvent is brought tothe surface in step 120, various separation steps can take place toseparate the bitumen, first solvent, and water. Any suitable separationunit or series of separation units can be used to separate the bitumen,first solvent, and water, such as distillation towers. Once separated,the bitumen can be further processed, such as by being subjected toupgrading to produce useful lighter hydrocarbons. The recovered firstsolvent can be reused in the bitumen extraction process, such as byreusing the first solvent in step 110.

Steps 110 and 120 described above can be repeated several times prior tomoving on to the injection of a second solvent. Performing multiplecycles of injecting first solvent and withdrawing a mixture of firstsolvent and bitumen can help to improve the overall amount of bitumenrecovered using the methods described herein.

In some embodiments, step 120 will not be capable of withdrawing all ofthe first solvent injected into the deposit of bituminous material instep 110. For example, from 10 to 50% of the first solvent injected intothe deposit of bituminous material may remain in the deposit after thecompletion of step 120. For environmental and economical reasons,additional steps should be taken to attempt to remove the first solventfrom the deposit of bituminous material.

In steps 130 and 140, a second solvent is injected into the bituminousmaterial to form a mixture of first solvent and second solvent, and thenthe mixture of first solvent and second solvent is withdrawn from thelaterally confined deposit of bituminous material. The second solvent isinjected into the bituminous material in an effort to mix with and/ordisplace the first solvent. Injection of the second solvent can resultin the second solvent pushing the residual first solvent towards theproduction wells, where the production wells can then be used towithdraw the mixture of first solvent and second solvent. Additionally,the second solvent may dissolve further bitumen not dissolved by thefirst solvent, and therefore the injection of the second solvent canalso increase the bitumen extraction rate.

Any suitable solvent capable of mixing with and/or displacing the firstsolvent can be used as the second solvent. In some embodiments, thesecond solvent includes one or more aliphatic compounds that are capableof solvating bitumen and/or the first solvent. Suitable aliphaticcompounds can include compounds such as alkanes or alkenes. Any of thesealiphatic compounds can be functionalized or non-functionalized. In someembodiments, the second solvent includes one or more aliphatichydrocarbons having 3 to 5 carbon atoms. In some embodiments, the secondsolvent includes aliphatic hydrocarbons having no more than 5 carbonatoms. The second solvent can also include lower carbon paraffins, suchas cyclo- and iso-paraffins having 3 to 5 carbon atoms. Exemplary secondsolvents include, but are nor limited to, methane, ethane, propane,butane, and/or pentane, alkene equivalents of these compounds and/orcombinations and derivatives thereof.

In some embodiments, the second solvent is a polar solvent. Any polarsolvent capable of displacing the first solvent can be used in step 130.In some embodiments, the polar solvent may be an oxygenated hydrocarbon.Oxygenated hydrocarbons may include any hydrocarbons having anoxygenated functional group. Oxygenated hydrocarbons may includealcohols, ketones and ethers. Oxygenated hydrocarbons as used in thepresent application do not include alcohol ethers or glycol ethers.

Suitable alcohols for use as the polar solvent may include methanol,ethanol, propanol, and butanol. The alcohol may be a primary (e.g.,ethanol), secondary (e.g., isopropyl alcohol) or tertiary alcohol (e.g.,tert-butyl alcohol).

As noted above, the polar solvent may also be a ketone. Generally,ketones are a type of compound that contains a carbonyl group (C═O)bonded to two other carbon atoms in the form: R1(CO)R2. Neither of thesubstituents R1 and R2 may be equal to hydrogen (H) (which would makethe compound an aldehyde). A carbonyl carbon bonded to two carbon atomsdistinguishes ketones from carboxylic acids, aldehydes, esters, amides,and other oxygen-containing compounds. The double-bond of the carbonylgroup distinguishes ketones from alcohols and ethers. The simplestketone is acetone, CH3-CO—CH3 (systematically named propanone).

In some embodiments, the polar solvent is a polar solvent that ismiscible with the first solvent. By selecting a polar solvent that issoluble in the first solvent (or in which the first solvent is soluble),the polar solvent may form a homogenous mixture with the first solvent.As some bitumen may be present in the first solvent, the homogenousmixture may also include a bitumen content. This homogenous mixture ofpolar solvent and first solvent (and possibly bitumen) can then bewithdrawn from the deposit of bituminous material via the productionwells to help remove first solvent from the deposit.

The polar solvent or mixture of polar solvents can be economical andrelatively easy to handle and store. The polar solvent or mixture ofpolar solvents may also be generally compatible with refineryoperations.

The polar solvent need not be 100% polar solvent, although in someembodiments, the polar solvent is made up entirely of polar solvent. Thepolar solvent may include a mixture of polar compounds and non-polarcompounds. However, in some embodiments, the polar solvent used in step130 includes more than about 50 wt % polar solvent, and preferably morethan about 70 wt % polar solvent.

In some embodiments, the second solvent is a mixture of water andperoxide. Suitable peroxides for use as the second solvent include thosewhich produce oxygen micro-bubbles upon being mixed with hydrocarbonliquids or solids. Exemplary peroxides suitable for use as the secondsolvent include hydrogen peroxide, peroxide salts, and any compoundscapable of producing hydrogen peroxide on decomposition in water (e.g.,sodium percarbonate).

The presence of the peroxide in the water can help to remove bitumen andbitumen-laden solvent. The peroxide accomplishes this at least in partby altering surface conditions, such as reducing interfacial tensionbetween oil, water, and inorganic material of the bituminous deposit(including rocks). Reduced interfacial tension can, for example, helprelease bitumen from within pores in the bituminous deposit. Exothermicheat release associated with the use of the peroxides can also assist inremoval of bitumen and solvent due to the heat release decreasing theviscosity of the bitumen and solvent. The decreased viscosity of thesematerials improves flowability and drainage and ultimately makes thematerial easier to recover.

The oxygen micro-bubbles formed from the mixing of peroxide andhydrocarbon material can also be useful in stripping hydrocarbonmaterial such as bitumen from inorganic material (such as sand) in thebituminous deposit. It is believed that the oil stripped from the sandwill form a film on the oxygen micro-bubbles. The stripped bitumenmaterial can then be recovered in the same manner as other free bitumenin the bituminous deposit, i.e., by injecting additional wash materials(solvents or water) into the bituminous deposit to mix with the oxygenmicro-bubbles and carry the stripped bitumen out of the deposit viaproduction wells. The continuous injection of a second solvent includingwater and peroxide will continue to produce the oxygen micro-bubbleshaving bitumen films within the deposit of bituminous material andprovide additional free bitumen for recovery from subsequent in situwash cycles.

The ratio of peroxide to water injected into the deposit as a secondsolvent can be any suitable ratio that provides for the creation ofoxygen micro-bubbles upon mixing with hydrocarbon material. In someembodiments, a 10 to 60% concentration of peroxide in water is provided.

The manner of injecting second solvent is similar or identical to themanner in which the first solvent is injected into the deposit ofbituminous material. The same injection wells used for injecting firstsolvent can be used to inject second solvent. The amount of secondsolvent injected into the laterally confined deposit of bituminousmaterial can be any suitable amount of second solvent needed forremoving the first solvent. In some embodiments, the amount of secondsolvent injected into the deposit of bituminous material will depend onthe amount of first solvent in the deposit. The amount of second solventinjected into the deposit of bituminous material can also vary on thesize of the area being subjected to bitumen extraction. In someembodiments, the amount of second solvent injected into the depositranges from 5,000 to 25,000 bbls.

In some embodiments, the desired amount of second solvent is injectedinto the deposit of bituminous material and is then allowed to stay inthe deposit of bituminous material for a period of time beforeproduction wells are used to remove the mixture of first solvent andsecond solvent. In some embodiments, the second solvent is held in thedeposit of bituminous material for a period of from 1 day to 1 month.

The manner of withdrawing a mixture of first and second solvent fromwithin the deposit if bituminous material is similar or identical to themanner in which the mixture of first solvent and dissolved bitumen iswithdrawn from the deposit of bituminous material. The same productionwells used to withdraw disbit from the deposit can be used to withdraw amixture of first and second solvent from the deposit.

The fluid material withdrawn from within the deposit of bituminousmaterial in step 140 generally includes first solvent and secondsolvent. Other materials that can be present in the fluid materialinclude water, bitumen, and organic and inorganic solids. Generallyspeaking, the fluid material withdrawn in step 140 includes from 40 to75% first solvent, from 0 to 80% second solvent, from 0 to 5% water,from 25 to 60% bitumen, and less than 2% other materials. Theconstituency of the fluid withdrawn in step 140 can also change overtime as the second solvent reaches the well head. The rate ofwithdrawing the fluid material is generally not limited, and in someembodiments, the fluid is withdrawn from within the deposit ofbituminous material via the production wells at a rate of from about5,000 to 25,000 bbls/day.

Once the mixture of first solvent and second solvent is brought to thesurface in step 140, various separation steps can take place to separatethe first solvent from the second solvent. Any suitable separation unitor series of separation units can be used to separate the first solventfrom the second solvent. Once separated, the first solvent and thesecond solvent can both be reused in the extraction process, with thefirst solvent reused in step 110 and the second solvent reused in step130.

As with steps 110 and 120, steps 130 and 140 can be carried out multipletimes in order to improve bitumen extraction and solvent recovery rates.Also, step 130 can be followed by an agitation step similar or identicalto the agitation step performed after step 110 as described in greaterdetail above. Thus, in some embodiments, each time second solvent isinjected into the bituminous deposit, a gas injection or gas pulsationstep can be carried out in order to promote mixing between the injectedsecond solvent and the residual first solvent and bitumen located in thebituminous deposit.

In some embodiments, step 140 will not be capable of withdrawing all ofthe second solvent injected into the deposit of bituminous material instep 130. For example, from 10 to 50% of the second solvent injectedinto the deposit of bituminous material may remain in the deposit afterthe completion of step 140. For environmental and economical reasons,additional steps should be taken to attempt to remove the second solventfrom the deposit of bituminous material.

In steps 150 and 160, water is injected into the bituminous material todisplace the residual second solvent towards the production wells, wherethe second solvent and water may then be withdrawn from the laterallyconfined deposit of bituminous material. In embodiments where the secondsolvent is a polar solvent, the injection of water is especially usefulat displacing the second solvent towards the production wells due to thedifference in polarity between the polar solvent and water. The waterinjected into the deposit can be in the form of steam or as liquidwater.

The manner of injecting water is similar or identical to the manner inwhich the first solvent and second solvent is injected into the depositof bituminous material. The same injection wells used for injectingfirst solvent and second solvent can be used to inject water. The amountof water injected into the laterally confined deposit of bituminousmaterial can be any suitable amount of water needed for removing thesecond solvent. In some embodiments, the amount of water injected intothe deposit of bituminous material will depend on the amount of secondsolvent in the deposit. The amount of water injected into the deposit ofbituminous material can also vary based on the size of the area beingsubjected to bitumen extraction. In some embodiments, the amount ofwater injected into the deposit ranges from 3:1 to 10:1 on awater:bitumen ratio.

In some embodiments, the desired amount of water is injected into thedeposit of bituminous material and is then allowed to stay in thedeposit of bituminous material for a period of time before productionwells are used to remove the mixture of water and second solvent. Insome embodiments, the water is held in the deposit of bituminousmaterial for a period of from 1 day to 1 month.

In some embodiments, the water can include peroxide in order to improvethe solvent and bitumen recovery. Any suitable peroxide can be added tothe water used in step 150, including but not limited to, hydrogenperoxide. In some embodiments, the amount of peroxide included in thewater used in step 150 is 10 to 60%.

The addition of peroxide to the water is considered beneficial for tworeasons. Firstly, the peroxide improves the removal of residual solventform within the bituminous deposit. As discussed above, this is due atleast in part to the peroxide reducing interfacial tension betweenhydrocarbon material, water, and inorganic material. Secondly, theperoxide is believed to reduce the viscosity of bitumen, which improvesthe drainage of the bitumen from the deposit via the production wells.Peroxides are believed to reduce the viscosity of bitumen by oxidizingthe sulfur contained in the bitumen.

The use of peroxides to improve solvent and bitumen removal from thebituminous deposit is also beneficial because the peroxide does notleave behind harmful residual chemicals in the deposit. For example,when hydrogen peroxide is used in the water wash, the hydrogen peroxidewill break down to oxygen and water.

The manner of withdrawing a mixture of water and second solvent fromwithin the deposit if bituminous material is similar or identical to themanner in which the mixture of first solvent and dissolved bitumen andthe mixture of first solvent and second solvent is withdrawn from thedeposit of bituminous material. The same production wells used towithdraw disbit and mixtures of first and second solvent from thedeposit can be used to withdraw a mixture of water and second solventfrom the deposit.

The fluid material withdrawn from within the deposit of bituminousmaterial in step 160 generally includes water and second solvent. Othermaterials that can be present in the fluid material include water,bitumen, and organic and inorganic solids. Generally speaking, the fluidmaterial withdrawn in step 160 includes from 40 to 90% water, from 60 to95% second solvent, from 2 to 10% first solvent, from 2 to 10% bitumen,and less than 2% other materials. The constituency of the fluidwithdrawn in step 160 can change over time as the injected water reachesthe well head. The rate of withdrawing the fluid material is generallynot limited, and in some embodiments, the fluid is withdrawn from withinthe deposit of bituminous material via the production wells at a rate offrom about 500 to 2,000 bbls/day per well head (by gravity drainage).

Once the mixture of water and second solvent is brought to the surfacein step 160, various separation steps can take place to separate thewater solvent from the second solvent. Any suitable separation unit orseries of separation units can be used to separate the water from thesecond solvent. In embodiments where the second solvent is polarsolvent, separation may occur naturally or with minimal effort due tothe difference in polarity. Once separated, the second solvent can bereused in the extraction process.

Any water left in the deposit of bituminous material can remain in thedeposit, as the water is not an environmental concern. In someembodiments, 5 to 50% of the water injected into the deposit in step 150will remain in the deposit.

The above described method can be performed one or more times on aconfined deposit of bituminous material. Similarly, any one step orpairs of steps (e.g., step 110 and 120) can be repeated multiple timesbefore moving on to the next step of the method. Repeating certain stepsof pairs of steps may help to increase the bitumen extractionefficiency.

Once a confined deposit of bituminous material has been subjected to theabove-described in-situ bitumen extraction process, the same process canbe carried out on adjacent deposits of bituminous material. In someembodiments, one or more freeze walls established for carrying out thein-situ bitumen extraction process on a first deposit of bituminousmaterial can be re-used when confining an adjoining deposit ofbituminous material. For example, when a confined deposit of bituminousmaterial has a square shape, three of the freeze walls can bedecommissioned while a fourth wall can be used as the first wall of anew confined deposit of bituminous material located next to the firstdeposit.

Additional pretreatment steps can also be carried out prior to or duringthe method described above. For example, any of a variety of fracturingsteps or method to increase porosity can be carried out prior to any ofthe solvent injection steps in an attempt to create more passageways forsolvent and other materials to pass through.

Additionally, hot water or sloppy steam can be injected into the depositof bituminous material prior to or during the injection of the firstsolvent in an effort to soften the oil sands and the bitumen componentor create channels for the subsequently injected solvent to passthrough. In some embodiments, the injection wells can be adapted toallow for the simultaneous injection of water and solvent through thesame injection wells. The injection wells can be “composite” injectionwells that include multiple passage ways within the same general piping.With reference to FIG. 6, a composite injection well 600 can include aco-annular inner passage 610 and a co-annular outer passage 620, withthe inner passage 610 having injection ports 615 that extend through theouter passage to the exterior of the injection well 600. In this manner,steam or water can travel down the inner passage 610 of the injectionwell 600 and be injected into the deposit at the same time that solventpasses down the outer passage 620 of the injection well 600 and isinjected into the deposit through standard injection ports 625 in fluidcommunication with the outer passage 620.

The majority of the system used to carry out the in-situ bitumenextraction methods described herein is discussed above, including thevertical freeze walls, the optional horizontal freeze wall, theplurality of injection bores, and the plurality of production wells.Also discussed above are the separation units that can be provided,including the separator for separating disbit into bitumen and solvent,the separator for separating a mixture of first solvent and secondsolvent, a separator for separating a mixture of second solvent andwater, and distillation units for producing solvent from recoveredbitumen.

Additional components that can be part of the system include arefrigerant source, a first solvent source, a water source, and a secondsolvent source. Each source can include any type of supply vessel thatis capable of supplying the desired fluid needed for the method. Thesupply vessels may also include recycle inputs for receiving fluidmaterial that is recovered from the process and sent back into thesystem. The refrigerant source is in fluid communication with theinterconnected well bores used to establish the freeze walls and, when atwo loop system as described above is used, can include a recycle inputfor receiving refrigerant that has passed through the two loop systemback into the refrigerant source for storage and further use. The firstsolvent and water sources can be in fluid communication with the outerand inner passage of a composite injection well, respectively.Additionally, the second solvent source can be in fluid communicationwith the injection well.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various other changes in the form anddetails may be made without departing from the spirit and scope of theinvention.

A presently preferred embodiment of the present invention and many ofits improvements have been described with a degree of particularity. Itshould be understood that this description has been made by way ofexample, and that the invention is defined by the scope of the followingclaims.

We claim:
 1. A method of in-situ bitumen extraction comprising: formingone or more vertical freeze walls within or around a deposit ofbituminous material and establishing a laterally confined deposit ofbituminous material; injecting a first solvent within the laterallyconfined deposit of bituminous material; withdrawing a mixture ofdissolved bitumen and first solvent from within the laterally confineddeposit of bituminous material; injecting a second solvent within thelaterally confined deposit of bituminous material; withdrawing a mixtureof first solvent and second solvent from within the laterally confineddeposit of bituminous material; injecting water within the laterallyconfined deposit of bituminous material; and withdrawing a mixture ofsecond solvent and water from within the laterally confined deposit ofbituminous material.
 2. The method as recited in claim 1, wherein themethod further comprises forming one or more horizontal freeze wallswithin the deposit of bituminous material and vertically confining thelaterally confined deposit of bituminous material.
 3. The method asrecited in claim 1, wherein the one or more vertical freeze walls abutan impervious geological material located (within or) below the depositof bituminous material.
 4. The method as recited in claim 1, whereinforming one or more vertical freeze walls within or around the depositof bituminous material comprises: drilling a plurality of spaced apartvertical bores within or around the deposit of bituminous material; andcirculating a refrigerant through the vertical bores.
 5. The method asrecited in claim 1, wherein injecting the first solvent within thelaterally confined deposit of bituminous material comprises: drillingone or more vertical injection bores within the laterally confineddeposit of bituminous material; and injecting the first solvent withinthe laterally confined deposit of bituminous material through the one ormore vertical injection bores.
 6. The method as recited in claim 5,wherein withdrawing the mixture of dissolved bitumen and first solventfrom within the laterally confined deposit of bituminous materialcomprises: drilling one or more vertical production bores within thelaterally confined deposit of bituminous material; and withdrawing themixture of dissolved bitumen and first solvent from the laterallyconfined deposit of bituminous material through the one or more verticalproduction bores.
 7. The method as recited in claim 1, wherein prior toinjecting the first solvent within the laterally confined deposit ofbituminous material, water is injected into the laterally confineddeposit of bituminous material.
 8. The method as recited in claim 7,wherein the water comprises steam.
 9. The method as recited in claim 5,wherein injecting the second solvent within the laterally confineddeposit of bituminous material comprises injecting the second solventthrough the one or more vertical injection bores.
 10. The method asrecited in claim 6, wherein withdrawing the mixture of first solvent andsecond solvent from within the laterally confined deposit of bituminousmaterial comprises withdrawing the mixture of first solvent and secondsolvent through the one or more vertical production bores.
 11. Themethod as recited in claim 5, wherein injecting water within thelaterally confined deposit of bituminous material comprises injectingwater through the one or more vertical injection bores.
 12. The methodas recited in claim 6, wherein withdrawing the mixture of second solventand water from within the laterally confined deposit of bituminousmaterial comprises withdrawing the mixture of second solvent and waterthrough the one or more vertical production bores.
 13. The method asrecited in claim 1, wherein the first solvent comprises an aromaticsolvent.
 14. The method as recited in claim 1, wherein the secondsolvent comprises a polar solvent.
 15. The method as recited in claim 6,wherein: the one or more vertical injection bores are arranged in astraight line; the one or more vertical production bores are arranged ina straight line parallel to and spaced a distance away from the straightline of vertical injection bores; and the first solvent is injected intothe laterally confined deposit of bituminous material in a directiontowards the straight line of one or more vertical production bores. 16.The method as recited in claim 1, further comprising: separating themixture of dissolved bitumen and first solvent withdrawn from within thelaterally confined deposit of bituminous material into a bitumen streamand a first solvent stream; and reusing the first solvent stream in thestep of injecting first solvent within the laterally confined deposit ofbituminous material.
 17. A system for in-situ bitumen extractioncomprising: a plurality of vertical freeze wall bores formed in adeposit of bituminous material and aligned in a geometric pattern; arefrigerant source in fluid communication with the plurality of verticalfreeze wall bores; a plurality of vertical injection bores formed winthe deposit of bituminous material and located within the geometricpattern of the plurality of freeze walls; a water source in fluidcommunication with the plurality of vertical injection bores; a solventsource in fluid communication with the plurality of vertical injectionbores; a second solvent source in fluid communication with the pluralityof vertical injection bores; and a plurality of vertical productionwells formed in the deposit of bituminous material and located withinthe geometric pattern of the plurality of freeze walls.
 18. The systemas recited in claim 17, further comprising: a bitumen-first solventseparator in fluid communication with the plurality of verticalproduction wells; a first solvent-second solvent separator in fluidcommunication with the plurality of vertical production wells; and asecond solvent-water separator in fluid communication with the pluralityof vertical production wells.
 19. The system as recited in claim 17,wherein the plurality of vertical freeze wall bores are in fluidcommunication with one another.
 20. The system as recited in claim 17,wherein the plurality of vertical injection bores each comprises: aninner passage; a co-annular outer passage separated from the innerpassage by a partition; a plurality of inner passage injection portsextending from the inner passage to the exterior of the verticalinjection bore; and a plurality of outer passage injection portsextending to the exterior of the vertical injection bore.
 21. The systemas recited in claim 20, wherein the inner passage is in fluidcommunication with only the water source and the outer passage is influid communication with only the first solvent source and the secondsolvent source.